Changing texture slot mapping size has no effect
why you expect changing size or offset values to be affecting rotation or flipping? Btw, if you use "UV" as mapping coordinates, you should use a  UV map, which would give better texturing control on your object... (later on this)

If you try, eg, "global" coordinates (projection "flat" in my example using a plane mesh):



you can invert X/Y slots and get the texture rotated...



is this what you want?

If you used UV mapping (you have to "UV unwrap" before your mesh in edit mode) instead:

you could assign your texture to that UV map, in the UV/image editor (on the left below), then set the UV mapping type using your unwrapped UV:



then, rotating the UV map in the UV/image editor, you can use the UV map and rotate, scale, modify it, to adjust your texture precisely, to your mesh:



Most people use UV mapping because it gives total freedom, but the other (old) way still works, it is just different.